<!DOCTYPE html>
<html>
<head>
<script src="http://libs.baidu.com/jquery/1.10.2/jquery.min.js"></script>
<script type="text/javascript"> 
var countdown=60; 
function settime(obj) {
    if (countdown == 0) {
        obj.removeAttribute("disabled");
        obj.value="免费获取验证码"; 
        countdown = 60; 
        return;
    } else {
        obj.setAttribute("disabled", true);
        obj.value="重新发送(" + countdown + ")";
        countdown--; 
    }
setTimeout(function() {
    settime(obj) }
    ,1000) 
}

</script>
<body> 
<input type="button" id="btn" value="免费获取验证码" onclick="settime(this)" /> 
   
</body>
</html>